The invention relates to a braking pressure modulator.
German patent document DE 42 27 084 A1 discloses a braking pressure modulator, designated therein as a pressure regulating module.
This known patent shows a two-channel pressure regulating module in FIG. 2 in which a common 3/2-way solenoid valve (therein 12) is provided as a reversing valve that connects both channels via a line (therein 15) either to the supply pressure (therein 17) in the actuated state of the valve 12, or to a control pressure (therein 13) in the non-actuated state of the valve 12. For purposes of this discussion, it shall be assumed that the 3/2-way solenoid valve 12 of DE 42 27 084 A1 is actuated, so that the supply pressure is being supplied to the other solenoid valves in FIG. 2. This represents the case of pressure regulation.
One of the two symmetrically configured pressure regulating circuits in DE 42 27 084 A1, i.e., the one containing the valves 9xe2x80x2, 7 and 3, is now considered. The 3/2-way solenoid valve (therein 9xe2x80x2) determines the direction of any pressure change in this circuit. In the non-actuated state of valve 9xe2x80x2 (as shown in FIG. 2 therein), a pressure increase takes place in this circuit since the supply pressure 17 is taking effect. In the actuated state of valve 9xe2x80x2, a pressure lowering takes place due to the connection of valve 9xe2x80x2 to the exhaust (therein 11xe2x80x2). The 2/2-way solenoid valve (therein 7) is connected in series to the valve 9xe2x80x2 and either establishes a connection to a control inlet of the downstream relay valve (therein control inlet 5) in its non-actuated state (as shown in FIG. 2), or closes off this control inlet in its actuated valve position.
Due to the series connection of the two valves 7 and 9xe2x80x2, these must jointly be brought into a given state in order to achieve a desired pressure change at the control inlet 5. Thus, they are not independent of each other but can only be operated simultaneously and together. This represents a cost disadvantage because the utilization of a 3/2-way solenoid valve with reversing function (i.e., valve 9xe2x80x2), and the requirement of great tightness in fitting at the two corresponding valve seats, are relatively expensive.
It is therefore the object of the invention to modify a pre-engagement unit of a braking pressure modulator of this type in such manner that the manufacturing costs are reduced.
This object is achieved in a pre-engagement unit for a braking pressure modulator for a pressure regulating circuit of an electronic braking system. The inventive pre-engagement unit comprises a first pneumatic inlet through which a supply pressure is supplied to the pre-engagement unit, a second pneumatic inlet through which a redundancy pressure is supplied to the pre-engagement unit, a first pneumatic output terminal through which the pre-engagement unit is connected to an air quantity augmenting relay valve, a second pneumatic output terminal through which the pre-engagement unit is connected to a pressure sink, and an electrically actuated valve system. The electrically actuated valve system comprises three substantially identical 2/2-way solenoid valves. Each of the 2/2-way solenoid valves includes first and second pneumatic terminals, and an electric terminal which is connected to an electronic control system of the electronic braking system for selective actuation of the 2/2-way solenoid valves. The first and second terminals of the 2/2-way solenoid valves are selectively connected to the pneumatic inlets and output terminals of the pre-engagement unit and to each other so that the first 2/2-way valves serves as an air admission valve for supply pressure to the pressure regulating circuit, the second 2/2-way solenoid valve serves as an air admission/exhaust valve for redundancy pressure to the pressure regulating circuit, and the third 2/2-way solenoid valve serves as an exhaust valve for the pressure regulating circuit. Thereby, the pressure in the pressure regulating circuit can be increased, decreased, or maintained. Desirably, the first, second, and third 2/2-way solenoid valves are connected in parallel to each other.
In the known patent document DE 42 27 084 A1, the suggestion is made through various embodiments to achieve economy by reducing the number of solenoid valves and thereby to save on pneumatic channels and similar components. The present invention abandons the idea to a great extent that the number of solenoid valves as such is the most important factor in saving costs. In the present invention, the average number of 3 solenoid valves per channel is even slightly greater than the average number of 2.5 solenoid valves per channel in the known patent. Instead, the invention emphasizes a novel valve design and a pneumatic circuit by means of which the solenoid valves of this novel valve design can be operated optimally.
The invention has the advantage that the pre-engagement unit of a pressure regulating circuit has three 2/2-way solenoid valves of very similar configuration connecting in parallel to each other rather than a 3/2-way solenoid valve connected in series to a 2/2-way solenoid valve.
By contrast to the known patent, in which a 3/2-way solenoid valve (therein 9xe2x80x2) is used as a reversing valve which leads to a reduced pulsating rate due to the design of such valves, the invention also has the advantage of an improved response time.
Because of the similarity of the 2/2-way solenoid valves, the armatures and the solenoid valves are standardized in another further development of the invention and, by using armatures of the same type made in larger quantities, costs are reduced.
Thus, three 2/2-way solenoid valves can be combined in one pre-engagement unit of a pressure regulating circuit and based on another further development of the invention, the magnet coils which are of identical construction, including the armatures, can be combined into the compact assembly of a triple magnet coil unit which can be extrusion coated (according to another further development of the invention). The triple magnet coil unit is thus available as a pre-assembled unit for integration into the electronic system of a braking pressure modulator. According to another further development, the magnet coil assembly interfaces with the electronic system advantageously by means of simply being plugged in.
Another further development of the invention has the advantage that the armatures can be made in a particularly space-saving manner by employing sealing seats that form metal-to-metal seals when the solenoid valves are under current. The utilization of such sealing seats is made possible by a specially designed pneumatic circuitry system.